Variable focal length lens system suitable for 35 mm. cameras



350-427 SR sumun KU\ I 0 April 1970 YASUO TAKAHASHI 3,506,337

VARIABLE FOCAL LENGTH LENS SYSTEM SUITABLE,FOR 35 MM CAMERAS Filed Sept.6. 1967 3 Sheets-Sheet 1 5/ 2 0 FIG. lb

6 F\. W A v INVENTOR )hsw ihknxmsm ATTORNEY April 1970 Sue TAKAHASHI3,506,337

VARIABLE FOCAL LENGTH LENS SYSTEM SUITABLEIOR, 55 MM CAMERAS INVENTORV4500 72/(4l/fl3/l/ 1M4, Mm

A'ITORNEY April 1970 YASUO TAKAHASHI 3,506,337

VARIABLE FOCAL LENGTH LENS SYSTEM SUITABLEFOR 35 MM CAMERAS Filed Sept.6, 1967 3 Sheets-Sheet 5 ATTORNEY United States Patent Oflice 3,506,337Patented Apr. 14, 1970 3,506,337 VARIABLE FOCAL LENGTH LENS SYSTEMSUITABLE FOR 35 MM. CAMERAS Yasuo Takahashi, Tokyo-to, Japan, assignorto Asahi Kogaku Kogyo Kabushiki Kaisha, Tokyo-to, Japan Filed Sept. 6,1967, Ser. No. 665,831

Claims priority, application Japan, Sept. 14, 1966,

41/ 60,692 Int. Cl. G02b 15/16, 11/34 US. Cl. 350-184 1 Claim ABSTRACTOF THE DISCLOSURE A simple zoo lens system of good opticalcharacteristics includes successively a stationary first lens group ofthree successive negative, positive and positive lenses, an axiallymovable second lens group of three successive negative, negative andpositive lenses the latter two lenses forming a cemented unit, a thirdlens group of two successive negative and positive lenses, the negativelens being axially movable, and a fourth stationary triplet lens groupsof three successive positive, negative and positive lenses, the lenssystem satisfying the following conditions:

wherein,

F is the resultant length of the first three lenses;

1, is the focal length of the ninth lens;

f is the resultant focal length of the ninth and tenth lenses;

r r and r are the radii of curvatures respectively of the front face ofthe fourth lens, the front face of the seventh lens, and the rear faceof the eighth lens; and

7 v v and 11 are the Abb values of the first second and third lensesrespectively.

BACKGROUND OF THE INVENTION cordingly, zoom lenses for pictures of 35mm. frame size or larger have found only a very limited application.

SUMMARY OF THE INVENTION It is a principal object of the presentinvention to provide an improved lens system.

Another object of the present invention is to provide an improvedvariable focal length or zoom lens system.

Still another object of the present invention is to provide an improvedzoom lens system which is highly suitable as an objective for theconventional 35 mm. camera.

A further object of the present invention is to provide an improved lenssystem of the above nature characterized by the small number of lensrequired and the consequent simplicity and low cost, a wide range offocal length variation, and a high degree of compensation and correctionover its focal length variation in spite of the small number of lensesemployed.

In a sense the present invention contemplates the provision of avariable focal length lens system comprising eleven lenses andsatisfying the following conditions:

F is the resultant length of the first three lenses;

1, is the focal length of ninth lens;

f is the resultant focal length of the ninth and tenth lenses;

r r and r are the radii of curvatures respectively of the front face ofthe fourth lens, the front face of the seventh lens, and the rear faceof the eighth lens; and

v v and 11 are the Abb or 1 values of the first, second and third lensesrespectively.

The first three lenses define a first stationary group in which thefirst lens is negative and the second and third lens are positive; thefourth lens is negative, and the fifth and sixth lenses are negative andpositive respectively and form a cemented unit with complimenting matingfaces, the fourth, fifth and sixth lenses constituting an axiallymovable second group; the seventh lens is negative and is individuallyaxially movable and with the positive eighth lens defines a third group;and the ninth, tenth and eleventh lenses define a stationary fourthgroup of the triplet type including positive ninth and eleventh lensesand a negative tenth lens. The second lens group is movable for focallength variation and the seventh lens is movable to maintain astationary focal plane. The lens system is mounted in a barrel ofconventional construction provided with cylindrical cams of knownstructure for moving the second lens group and the seventh lens in acoupled related manner so as not to shift the focal plane with avariation in the lens system focal length.

The above designated condition (1) functions to correct coma aberrationwith respect to rays of greater ray heights in the relative short focallength range of the lens system and also functions to balance the sinecondition over the full local length range of the lens system.

Condition (2) serves to suitably balance spherical aberation and tosuitably correct coma aberration by balancing r and r Condition (3)restricts the range of condition (2) whereby to maintain sphericalaberration and coma aberration in a properly corrected state.

Conditions (4) and function to provide the lens system with a Pezval sumsuitable for the object over the full focal length range.

Condition (6) functions to balance chromatic aberration in the firstlens group and also to well balance the various aberrations which areinclined to be influenced by the action to maintain chromatic differenceof magnification in a suitably corrected state over the whole lenssystem.

The zoom lens system of the present invention is of simple construction,requiring only eleven lenses, and in spite of this possesses a highdegree of correction over a wide variation in focal length.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURES 1(a), 1(b) and 1(0) arelongitudinal sectional views of a lens system embodying the presentinvention and illustrated at minimum focal length, intermediate focallength and maximum focal length adjustments respectively; and

FIGURES 2(a), 2(b) and 2(0) are sets of aberration curves at minimumfocal length, intermediate focal length and maximum focal lengthadjustments respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingsand particularly FIG- URE 1 thereof which illustrates a preferredembodiment of the present invention shown adjusted to minimum,intermediate and maximum focal lengths, the improved lens systemincludes eleven successive coaxially related lens 1 to 11 respectivelyarranged in four successive lens groups G1 to G4. Lens group G1 includeslenses 1, 2 and 3; lens group G2 includes lenses 4, 5 and 6; lens groupG3 includes lenses 7 and 8; and lens group G4 is of the triplet type andincludes lenses 9, and 11. Conventional means are provided, asaforesaid, to relatedly axially move lens group G2 and lens 7 to varythe lens system focal length and maintain its focal plane stationary.

The first lens 1 is negative and has a thickness d an index ofrefraction n a front face of radius of curvature r and a rear face ofradius of curvature r the second lens 2 is positive and spaced from thefirst lens 1 a distance d and has a thickness d;,, an index ofrefraction n a front face of radius of curvature r and a rear face ofradius of curvature r and the third lens 3 is positive and is spaced adistance 4 from the second lens 2 and has a thickness d an index ofrefraction 11 a front face of radius of curvature r and a rear face ofradius of curvature r The fourth lens 4 is negative and is spaced avariable distance d from the third lens 3 and has a thickness d an indexof refraction n a front face of radius of curvature r and a rear face ofradius of curvature 1' and the fifth and sixth lens are a cemented unitwith contiguous confronting mating faces, the fifth lens being negativeand being spaced from the fourth lens 4 a distance d and having athickness d and index of refraction 11 a front face of radius ofcurvature r and a rear face of radius of curvature r and the sixth lensbeing positive and abutting and cemented to the fifth lens 5, and havinga thickness d an index of refraction m a front face of radius ofcurvature r and a rear face of radius of curvature r The seventh lens 7is negative lens and is spaced a variable distance d from the sixth lens6 and has a thickness d an index refraction n a concave front face ofradius of curvature r and a convex rear face of radius of curvature rand the eighth lens 8 is positive and spaced a variable distance 1 fromthe seventh lens 7 and has a thickness d an index of refraction n afront face of radius of curvature r and a rear face of radius ofcurvature r The ninth lens 9 is positive and spaced from the eighth lens8 a distance d and has a thickness d an index of refraction n a convexfront face of radius of curvature r and a rear face of radius ofcurvature r the tenth lens 10 is negative and spaced from the ninth lensa distance d and has a thickness d an index of refraction n a concavefront face of radius of curvature r and a concave rear face of radius ofcurvature r and the eleventh lens 11 is positive and is spaced adistance d from the tenth lens 10 and has a thickness d an index ofrefraction n a front face of radius of curvature r and a convex rearface of radius of curvature r It should be noted that distances betweenlenses are axially measured between the confronting faces of adjacentlenses and the lens thicknesses are also axially measured.

The following Table 1 sets forth the dimensions and parameters of aspecific example of the present lens system having a focal lengthvariable between mm. and 205 mm. The radii of curvatures r of the lensfaces, and the lens spacings and thicknesses a are as above designated,and the indices of refraction n and the Abb numbers n are the numeratorsand denominators respectively of the correspondingly designated lensrefractive indices n TABLE 1 d2 1. 50 Tl 3, 000. 000

d 1. 50 m 1. 66680/38. 1 r2 91. 640

(is 4. 50 71,3 1. 61405/55. 1 T4 4, 545. 063

do 2. 0O-64. 78 n 14.5. 000

d1 1. 00 m 1. 51633/64. 1 r 127. 275

de 2. 50 n 350. 000

(in 3. 00 m 1. 74077/27. 7 104. 599

o 2. 00 m 1. 66446/35. 9 H3 -72. 889

lfi 0. 10 53. 000

die 5. 30 m 1. 62041/60. 3 717 152. 064

413 2. 50 Tim 1. 64769/33. 9 Tli 53. 698

(in 18. 50 T20 1, 000. 000

(I10 5. 00 m 1. 58913/61- 2 m 46. 238

The following Tables 2 and 3 set forth the Seidel coefficients of thelens system of the specific example of Table I, with a stop positionedbetween the ninth lens 9 and the tenth lens 10, Table 2 being for thelens system adjusted to minimum focal length and Table 3 being for lenssystem adjusted to maximum focal length.

TABLE 2 S1 S2 S: P S5 0. 000 O. 007 011 O. 664 0. 185 O. 022 O. 371 O.047 O. 101 O. 007 O. 310 O. 025 O. 010 O. 065 O. 007 O. 436 0. 081 0.024 0. 319 0. 104 O. 259 0. 618 0. 043 1. 577 0. 697 1. 122 O. 199 2.129 O. 096 O. 055 O. 227 O. 163 O. 003 O. 054 O. 094 O. 599 O. 297 0.094 0. 068 O. 051 O. 107 O. 007 0. 345 0. 023 O. 437 O. 172 0. 678 O.336 U. 238 -11. 250 O. 465 O. 225 1. 086 0. 327 O. 082 0. 123 1. 138 0.399 0. 422 O. 288 1. 249 0. 212 0. 614 U. 140 5. 891 1. 445 0. 214 O.407 6. 343 O. 864 O. 739 0. 218 2. 119 O. 878 O. 622 O. 522 0. 222 0.330 0. 331 0. 539 0. 021 0. 000 0. 681 0. 000 0. 538 0. 670 O. 033

TABLE 3 S2 S P S5 0. 001 O. 013 027 O. 707 12. 508 7. 194 O. 895 4. 65410. 398 5. 793 0. 771 3. 658 O. 050 0. 098 O. 017 O. 227 1. 512 O. 6040. 772 O. 550 2. 318 3. 506 0. 105 5. 462 2. 441 2. 622 O. 481 3. 335 O.115 O. 165 O. 548 1. 024 0. 095 O. 321 O. 228 1. 847 0. 073 0. 003 0.165 0. 007 1. 083 O. 589 O. 834 0. 775 0. 437 O. 417 1. 638 1. 960 0.236 O. 605 1. 123 1. 316 1. 086 0. 791 0. 199 0. 720 1. 138 0. 963 1.020 1. 679 1. 249 0. 512 1. 482 0. 817 5. 891 3. 489 0. 516 2. 372 6.343 2. 087 1. 784 1. 274 -2. 119 2. 120 1. 502 3. 625 0. 222 0. 799 O.076 3. 141 0. 021 0. 000 1. 645 0. 004 511111. O. 875 0. 092 220 0. 0812. 219

As seen in FIGURES 2(a), (b) and (c) of the drawings which illustratethe spherical aberration and sine condition, chromatic aberration,distortion, and astigmatism curves of the specific lens system atminimum, intermediate and maximum focal length, highly suitablecorrection in a Zoom lens system is effected over the full focal lensvariation range in spite of the fact that only eleven lenses areemployed.

While there has been described and illustrated a preferred embodiment ofthe present invention, it is apparent that numerous alterations,omissions and additions may be made without departing from the spiritthereof.

I claim:

1. A variable focal length lens system comprising eleven lensesconsecutively designated as the first to the eleventh lens, the fifthand sixth lenses constituting a cemented doublet, the lens faces beingconsecutively designated as the first to the twenty-first face with theconfronting mating surfaces of the fifth and sixth lenses defining asingle lens face, and possessing the following dimensions andparameters:

d 1. 50 m 1. 66680/33. 1 T2 91. 640

(it 0. 10 f5 102. 000

do 2. 00-64. 78 T 145. 000

1 1. 00 m l. 51633/64. 1 Ta 127. 275

de 2. 50 To 350. 000

do 1. 00 m 1. 64000/60. 2 43. 860

(in 3. 00 m 1. 74077/27. 7 104. 599

ll 68. 50-5. 72 T11 50. 000

dn 4. 00 ns 1. 51633/64. 1 n5 68. 458

die 5. n 1. 62041/60. 3 n 152. 064

d 2. m0 1. 64769/33. 9 Tu; 53. 698

ie 18. 50 no 1, 000. 000

20 5. 00 7L1; l. 58913/61. 2 T2 46. 238

wherein r, is the radius of curvature of the ith lens face, a is thedistance between the ith lens face and the next successive lens face,and n is the index of refraction and Abb value of the nth lens, thefourth, fifth and sixth lenses being axially movable as a group and theseventh lens being axially movable.

References Cited UNITED STATES PATENTS 3,074,318 1/1963 Yamaji 350184FOREIGN PATENTS 1,008,309 10/1965 Great Britain.

JOHN K. CORBIN, Primary Examiner US. Cl. X.R. 350-214

